This is an observational, 48-week study of lean body mass, appetite, functional performance, and systemic markers of inflammation during highly active antiretroviral therapy (HAART) in subjects co-enrolled in ACTG antiretroviral studies. The study will determine if changes in body composition are related to changes in HIV-1 RNA levels and whether the magnitude of these changes in body composition is quantitatively related to risks for AIDS-defining complications. There are no wasting or weight criteria for entry into this study except that subjects must be < or = to 28 kg/m2.